U.S. patent number 9,101,330 [Application Number 14/265,181] was granted by the patent office on 2015-08-11 for real-time x-ray monitoring.
This patent grant is currently assigned to CONSENSYS IMAGING SERVICE, INC.. The grantee listed for this patent is Consensys Imaging Service, Inc.. Invention is credited to James Gessert, Mike M. Tesic.
United States Patent |
9,101,330 |
Tesic , et al. |
August 11, 2015 |
Real-time X-ray monitoring
Abstract
A medical imaging system has a radiation source, a radiation
sensor, a data-collection unit, and an imaging system. The
radiation source has an opening to direct a collimated radiation
beam in a direction towards a patient. The radiation sensor is
disposed proximate the opening and within the collimated radiation
beam to measure a fluence of the collimated radiation beam. The
data-collection unit is disposed to collect radiation from the
collimated beam after interaction with the patient. The imaging
system is in communication with the data-collection unit and
configured to generate an image of a portion of the patient from
the collected radiation.
Inventors: |
Tesic; Mike M. (Superior,
CO), Gessert; James (Loveland, CO) |
Applicant: |
Name |
City |
State |
Country |
Type |
Consensys Imaging Service, Inc. |
Cary |
IL |
US |
|
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Assignee: |
CONSENSYS IMAGING SERVICE, INC.
(Cary, IL)
|
Family
ID: |
47174920 |
Appl.
No.: |
14/265,181 |
Filed: |
April 29, 2014 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20140254761 A1 |
Sep 11, 2014 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13112829 |
May 20, 2011 |
8714818 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05G
1/42 (20130101); H05G 1/44 (20130101); A61B
6/58 (20130101); G01T 1/201 (20130101); A61B
6/542 (20130101); G01N 23/046 (20130101); A61B
6/488 (20130101); G01N 2223/612 (20130101); G01N
2223/419 (20130101); A61B 6/54 (20130101); G01T
1/023 (20130101) |
Current International
Class: |
H05G
1/42 (20060101); H05G 1/44 (20060101); A61B
6/02 (20060101); A61B 6/00 (20060101); G01T
1/20 (20060101); G01N 23/04 (20060101); G01T
1/02 (20060101) |
Field of
Search: |
;378/4-20,95-97,108,162,165,204,207,210,901
;250/354.1,358.1,359.1,360.1,370.01,370.06,370.07,370.08,3,70.09,370.11,371,394,395,206,208.1,227.29,227.31 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Midkiff; Anastasia
Attorney, Agent or Firm: Christensen; Kory D. Stoel Rives
LLP
Claims
What is claimed is:
1. A medical imaging system comprising: a radiation source having
an opening to direct a collimated radiation beam in a direction
towards a patient; a radiation sensor disposed proximate the
opening and within the collimated radiation beam to measure a
fluence of the collimated radiation beam; a data-collection unit
disposed to collect radiation from the collimated radiation after
interaction with the patient; an imaging system in communication
with the data-collection unit and configured to generate an image
of a portion of the patient from the collected radiation; and a
monitoring system in communication with the radiation sensor, the
monitoring system comprising instructions to determine, during
patient imaging, an estimate of an effective radiation dose
delivered to the patient during an imaging procedure with the
medical imaging system from the measured fluence.
2. The medical imaging system recited in claim 1 wherein the
radiation sensor comprises: a scintillating fiber that emits light
in response to absorption of a photon of radiation by the
scintillating fiber; and a photodetector coupled with the
scintillating fiber to detect emission of light by the
scintillating fiber.
3. The medical imaging system recited in claim 2 wherein: the
scintillating fiber comprises a plurality of scintillating fibers
arranged substantially parallel to each other; and the
photodetector comprises a plurality of photodetectors, each of the
plurality of photodetectors being coupled with one of the plurality
of scintillating fibers.
4. The medical imaging system recited in claim 1 wherein the
radiation sensor comprises: a first radiation sensor having: a
first plurality of scintillating fibers arranged substantially
parallel to each other and to a first direction, each of the first
plurality of scintillating fibers emitting light in response to
absorption of a photon; and a first plurality of photodetectors,
each of the first plurality of photodetectors coupled with one of
the first plurality of scintillating fibers to detect emission of
light by the one of the first plurality of scintillating fibers;
and a second radiation sensor having: a second plurality of
scintillating fibers arranged substantially parallel to each other
and to a second direction, each of the second plurality of
scintillating fibers emitting light in response to absorption of a
photon; and a second plurality of photodetectors, each of the
second plurality of photodetectors coupled with one of the second
plurality of scintillating fibers to detect emission of light by
the one of the second plurality of scintillating fibers, wherein
the first and second directions are nonparallel.
5. The medical imaging system recited in claim 4 wherein the first
and second directions are substantially orthogonal.
6. The medical imaging system recited in claim 1 wherein the
radiation sensor measures a spatial distribution of the
fluence.
7. The medical imaging system recited in claim 1 wherein the
radiation sensor measures a spectral distribution of the
fluence.
8. The medical imaging system recited in claim 1 further comprising
a mechanism to effect relative translational and/or rotational
motion between the radiation source and the patient.
9. The medical imaging system recited in claim 8 wherein the
instructions to determine the estimate of the effective radiation
dose delivered to the patient comprise: instructions to obtain a
peak voltage applied to the radiation source to generate the
collimated radiation beam; instructions to obtain a measure of a
geometry of the medical imaging system; instructions to obtain a
measure of a size of the patient; and instructions to obtain a
measure of relative motion of the patient with respect to the
medical imaging system.
10. The medical imaging system recited in claim 9 further
comprising a host system in communication with the imaging system
and with the radiation source, wherein: the instructions to obtain
the peak voltage applied to the radiation source comprise
instructions to obtain the peak voltage applied to the radiation
source from the host system; the instructions to obtain the measure
of the geometry of the medical imaging system comprise instructions
to obtain the measure of the geometry of the medical imaging system
from the host system; the instructions to obtain the measure of the
size of the patient comprise instructions to obtain the measure of
the size of the patient from the host system; and the instructions
to obtain the measure of relative motion of the patient with
respect to the medical imaging system comprise instructions to
obtain the measure of relative motion of the patient with respect
to the medical imaging system from the host system.
11. The medical imaging system recited in claim 9 wherein the
instructions to obtain the peak voltage applied to the radiation
source comprise instructions to obtain the peak voltage applied to
the radiation source from the measured fluence of the collimated
radiation beam.
12. The medical imaging system recited in claim 9 further
comprising a geometry sensor, wherein the instructions to obtain
the measure of the geometry of the medical imaging system comprise
instructions to obtain the measure of the geometry of the medical
imaging system from the geometry sensor.
13. The medical imaging system recited in claim 12 wherein the
geometry sensor comprises a sensor selected from the group
consisting of an ultrasound sensor, a laser micrometer, and a
visual camera.
14. The medical imaging system recited in claim 9 further
comprising a patient size sensor, wherein the instructions to
obtain the measure of the size of the patient comprise instructions
to obtain the measure of the size of the patient from the
patient-size sensor.
15. The medical imaging system recited in claim 14 wherein the
patient-size sensor comprises a sensor selected from the group
consisting of an ultrasound sensor, a laser micrometer, and a
visual camera.
16. The medical imaging system recited in claim 9 further
comprising a motion sensor, wherein the instructions to obtain the
measure of relative motion of the patient with respect to the
medical imaging system comprise instructions to obtain the measure
of relative motion of the patient with respect to the medical
imaging system from the motion sensor.
17. The medical imaging system recited in claim 16 wherein the
motion sensor comprises a mechanical sensor, an electromagnetic
sensor, or an acoustic sensor.
18. The medical imaging system recited in claim 1 wherein the
monitoring system is further in communication with a central system
that is in communication with a second monitoring system remote
from the monitoring system.
19. The medical imaging system recited in claim 18 wherein the
monitoring system further has instructions to record the estimate
of the effective radiation dose delivered to the patient during the
imaging procedure at a data store coupled with the central
system.
20. The medical imaging system recited in claim 1 wherein the
monitoring system further has: instructions to identify the
measured fluence of the collimated radiation beam as being outside
an acceptable range; and instructions to initiate an alarm in
response to identifying the measured fluence being outside the
acceptable range.
21. The medical imaging system recited in claim 1 wherein the
monitoring the system further has: instructions to perform a
comparison of the measured fluence of the collimated radiation beam
with a record of prior measurements of fluence produced by the
radiation source; and instructions to estimate a time to failure of
the radiation source from the comparison.
22. A method of monitoring a medical imaging system comprising a
radiation source having an opening to direct a collimated radiation
beam in a direction towards a patient and an imaging system
configured to generate an image of a portion of the patient from
radiation collected from the collimated radiation beam after
interaction with the patient, the method comprising: measuring a
fluence of the collimated radiation beam with a radiation sensor
disposed proximate the opening and within the collimated radiation
beam; and determining, during patient imaging, an estimate of an
effective radiation dose delivered to the patient during an imaging
procedure with the medical imaging system from the measured
fluence.
23. The method recited in claim 22 wherein the radiation sensor
comprises: a scintillating fiber that emits light in response to
absorption of a photon of radiation by the scintillating fiber; and
a photodetector coupled with the scintillating fiber to detect
emission of light by the scintillating fiber.
24. The method recited in claim 23 wherein: the scintillating fiber
comprises a plurality of scintillating fibers arranged
substantially parallel to each other; and the photodetector
comprises a plurality of photodetectors, each of the plurality of
photodetectors being coupled with one of the plurality of
scintillating fibers.
25. The method recited in claim 22 wherein the radiation sensor
comprises: a first radiation sensor having: a first plurality of
scintillating fibers arranged substantially parallel to each other
and to a first direction, each of the first plurality of
scintillating fibers emitting light in response to absorption of a
photon; and a first plurality of photodetectors, each of the first
plurality of photodetectors coupled with one of the first plurality
of scintillating fibers to detect emission of light by the one of
the first plurality of scintillating fibers; and a second radiation
sensor having: a second plurality of scintillating fibers arranged
substantially parallel to each other and to a second direction,
each of the second plurality of scintillating fibers emitting light
in response to absorption of a photon; and a second plurality of
photodetectors, each of the second plurality of photodetectors
coupled with one of the second plurality of scintillating fibers to
detect emission of light by the one of the second plurality of
scintillating fibers, wherein the first and second directions are
nonparallel.
26. The method recited in claim 25 wherein the first and second
directions are substantially orthogonal.
27. The method recited in claim 22 wherein measuring the fluence of
the collimated radiation beam comprises measuring a spatial
distribution of the fluence.
28. The method recited in claim 22 wherein measuring the fluence of
the collimated radiation beam comprises measuring a spectral
distribution of the fluence.
29. The method recited in claim 22 wherein the medical imaging
system further comprises a mechanism to effect relative
translational and/or rotational motion between the radiation source
and the patient, the method further comprising: obtaining a peak
voltage applied to the radiation source to generate the collimated
radiation beam; obtaining a measure of a geometry of the medical
imaging system; obtaining a measure of a size of the patient; and
obtaining a measure of relative motion of the patient with respect
to the medical imaging system.
30. The method recited in claim 29 wherein: the medical imaging
system further comprises a host system in communication with the
imaging system, the radiation source, and the mechanism; obtaining
the peak voltage applied to the radiation source comprises
obtaining the peak voltage applied to the radiation source from the
host system; obtaining the measure of the geometry of the medical
imaging system comprises obtaining the measure of the geometry of
the medical imaging system from the host system; obtaining the
measure of the size of the patient comprises obtaining the measure
of the size of the patient from the host system; and obtaining the
measure of relative motion of the patient with respect to the
medical imaging system comprises obtaining the measure of relative
motion of the patient with respect to the medical imaging system
from the host system.
31. The method recited in claim 29 wherein: obtaining the peak
voltage applied to the radiation source comprises determining the
peak voltage applied to the radiation source from the measured
fluence; obtaining the measure of the geometry of the medical
imaging system comprises measuring the geometry of the medical
imaging system with a geometry sensor; obtaining the measure of the
size of the patient comprises measuring the size of the patient
with a patient-size sensor; and obtaining the measure of relative
motion of the patient with respect to the medical imaging system
comprises measuring the relative motion of the patient with respect
to the medical imaging system with a motion sensor.
32. The method recited in claim 22 further comprising transmitting
the estimate of the effective radiation dose delivered to the
patient during the imaging procedure to a central system for
storing the estimate.
33. The method recited in claim 22 further comprising: identifying
the measured fluence of the collimated radiation beam as being
outside an acceptable range; and initiating an alarm in response to
identifying the measured fluence being outside the acceptable
range.
34. The method recited in claim 22 further comprising: performing a
comparison of the measured fluence of the collimated radiation beam
with a record of prior measurements of fluence produced by the
radiation source; and estimating a time to failure of the radiation
source from the comparison.
35. The medical imaging system recited in claim 1 wherein the
medical imaging system is further configured to store the estimate
of the effective radiation dose delivered to the patient and
associate the stored estimate of the effective radiation dose with
the patient.
36. The medical imaging system recited in claim 1 wherein the
monitoring system comprises instructions to determine the estimate
of the effective radiation dose based on one or more of: a
probability of absorbing a photon based on a set of tissue
absorption characteristics; and a patient skin-air kerma.
37. The method recited in claim 22 further comprising storing the
estimate of the effective radiation dose delivered to the patient
and associate the stored estimate of the effective radiation dose
with the patient.
38. The method recited in claim 22 wherein determining the estimate
of the effective radiation dose comprises determining based on one
or more of: a probability of absorbing a photon based on a set of
tissue absorption characteristics; and a patient skin-air kerma.
Description
BACKGROUND OF THE INVENTION
This application relates to diagnostic radiation systems such as
x-ray systems. More specifically, this application relates to
methods and apparatus for monitoring the operation of diagnostic
radiation systems.
Ever since Wilhelm Rontgen discovered x rays and successfully
imaged his wife's hand to show the structure of her bones,
radiation has been used as a medical diagnostic tool. While
two-dimensional radiographs were used for decades, such images
suffered from the superposition of images of structures outside the
specific region of interest and were generally produced images that
were limited to particular image planes.
More recent advances have resulted in the development of
tomographic techniques, particularly as embodied in
computed-tomography ("CT") imaging devices and in computed axial
tomography ("CAT") imaging devices. Since their introduction in the
1970's, tomographic imaging devices have become widely used for
both diagnostic and preventive medical applications. In addition to
perform CT and CAT scans to confirm suspected diagnoses of tumors,
infarction, bone trauma, and the like, scanning using such devices
is now almost routine for patients at high risk for certain medical
conditions such as colon cancer and heart disease. Indeed, some
institutions offer full-body scans to the general public as part of
a generalized effort for early detection of disease.
While such efforts have had a significant impact in allowing
physicians to detect disease early and to confirm diagnoses without
invasive techniques, they are not without a number of concerns. One
particular concern results from the fact that x rays are a form of
ionizing radiation that have their own impact on the body being
measured. Since the early 1980's, the per capita dose of radiation
from medical imaging has increased by a factor of almost six. Some
estimates suggest that the current level of usage of CT scans will
result in an increase in cancer mortality rate of 1.5% to 2% from
cancers caused by the scans. While the benefit of reducing cancer
mortality from early detection of cancers significantly exceeds
this rate, it remains a concern.
Monitoring the actual dose delivered to patient is complicated by a
number of factors. The dose depends on multiple known factors that
include the volume and type of tissue scanned, the build of the
patient scanned, the number and type of scan sequences, and the
quality of images to be produced. There is, moreover, a lack of
uniformity among machines used to perform the scans, varying not
only among manufacturers but also being sufficiently complex
devices to have individual variations in uniformity. The dose
received by a patient depends on how the machines are used and how
different settings for a particular imaging session are
configured.
In addition to these patient concerns, there are concerns about the
machines themselves. The x-ray tube, for example, tends to degrade
over time as the machine is used. To obtain a similar image
quality, a machine tends to need to be operated at higher current
(mA) as the efficiency of the tube decreases. It is desirable to be
able to predict when tube operational quality is likely to become
so low that replacement is needed.
There are, thus, a number of deficiencies in the art that it is
desirable to address.
SUMMARY
Embodiments of the invention provide a medical imaging system that
has a radiation source, a radiation sensor, a data-collection unit,
and an imaging system. The radiation source has an opening to
direct a collimated radiation beam in a direction towards a
patient. The radiation sensor is disposed proximate the opening and
within the collimated radiation beam to measure a fluence of the
collimated radiation beam. The data-collection unit is disposed to
collect radiation from the collimated beam after interaction with
the patient. The imaging system is in communication with the
data-collection unit and configured to generate an image of a
portion of the patient from the collected radiation.
The radiation sensor may comprise a scintillating fiber that emits
light in response to absorption of a photon of radiation by the
scintillating fiber. A photodetector is coupled with the
scintillating fiber to detect emission of light by the
scintillating fiber. In some instances, the scintillating fiber may
comprise a plurality of scintillating fibers arranged substantially
parallel to each other and the photodetector may comprise a
plurality of photodetectors with each of the plurality of
photodetectors being coupled with one of the plurality of
scintillating fibers.
In some embodiments, the radiation sensor has two such arrangements
in different orientations. Specifically, the radiation sensor
comprises a first radiation sensor and a second radiation sensor.
The first radiation sensor has a plurality of scintillating fibers
arranged substantially parallel to each other and to a first
direction, with each of the first plurality of scintillating fibers
emitting light in response to absorption of a photon. Each of a
first plurality of photodetectors is coupled with one of the first
plurality of scintillating fibers to detect emission of light by
the one of the first plurality of scintillating fibers. The second
radiation sensor has a second plurality of scintillating fibers
arranged substantially parallel to each other and to a second
direction, with each of the second plurality of scintillating
fibers also emitting light in response to absorption of a photon.
Each of a second plurality of photodetectors is coupled with one of
the second plurality of scintillating fibers to detect emission of
light by the one of the second plurality of scintillating fibers.
The first and second directions are nonparallel. In a particular
embodiment, the first and second directions may be substantially
orthogonal.
The medical imaging system may additionally comprise a monitoring
system in communication with the radiation sensor. The monitoring
system has instructions to determine an estimate of an effective
radiation dose delivered to the patient during an imaging procedure
with the medical imaging system from the measured fluence. The
radiation sensor may measure a spatial distribution of the fluence
and/or it may measure a spectral distribution of the fluence. The
medical imaging system may also additionally comprise a mechanism
to effect relative translational and/or rotational motion between
the radiation source and the patient.
To determine the estimate of the effective radiation dose delivered
to the patient, a number of quantities may be obtained: a peak
voltage applied to the radiation source to generate the collimated
radiation beam, a measure of a geometry of the medical imaging
system, a measure of a size of the patient, and a measure of
relative motion of the patient with respect to the medical imaging
system. In one embodiment, the medical imaging system further
comprises a host system in communication with the imaging system
and with the radiation source, with each of these quantities being
obtained from the host system.
In other embodiments, each of the quantities is instead obtained
from an appropriate sensor also comprised by the medical imaging
system. For example, the peak voltage applied to the radiation
source may be obtained from the measured fluence of the collimated
radiation beam. This may include, for example, using spectral
information such as the half-value-layer-aluminum. The medical
imaging system may further comprise a geometry sensor, with the
measure of the geometry of the medical imaging system being
obtained from the geometry sensor; examples of suitable geometry
sensors include an ultrasound sensor, a laser micrometer, and a
visual camera. The medical imaging system may further comprise a
patient-size sensor, with the measure of the patient size being
obtained from the patient-size sensor; examples of patient-size
sensors also include an ultrasound sensor, a laser micrometer, and
a visual camera. The medical imaging system may further comprise a
motion sensor, with the measure of relative motion of the patient
with respect to the medical imaging system being obtained from the
motion sensor; the motion sensor might comprise a mechanical
sensor, an electromagnetic sensor, or an acoustic sensor. The
medical imaging system may further comprise a motion sensor for
determining gantry rotation.
The monitoring system may form part of a wider, centrally organized
system. Specifically, the monitoring system may be in further
communication with a central system that is in communication with a
second monitoring system remote from the monitoring system. In such
instances, the monitoring system may have instructions to record
the estimate of the effective radiation dose delivered to the
patient during the imaging procedure at a data store coupled with
the central system.
The monitoring system may also may have functionality in addition
to determine dose estimates. For example, the monitoring system may
identify the measured fluence of the collimated radiation beam as
being outside an acceptable range, initiating an alarm in response
to such an identification. In other instances, the monitoring
system may perform a comparison of the measured fluence of the
collimated radiation beam with a record of prior measurements of
fluence produced by the radiation source and thereby estimate a
time to failure of the radiation source from the comparison.
BRIEF DESCRIPTION OF THE DRAWINGS
A further understanding of the nature and advantages of the present
invention may be realized by reference to the remaining portions of
the specification and the drawings, wherein like reference labels
are used through the several drawings to refer to similar
components. In some instances, reference labels are followed with a
hyphenated sublabel; reference to only the primary portion of the
label is intended to refer collectively to all reference labels
that have the same primary label but different sublabels.
FIG. 1 provides a schematic overview of a CT scanning system as may
be used in embodiments of the invention;
FIG. 2 illustrates a system in which the CT scanning system
illustrated in FIG. 1 may be integrated;
FIG. 3 is a schematic illustration of a structure that may be used
for a monitoring system used as part of the CT scanning system of
FIG. 1;
FIG. 4 shows a structure that may be used for an x-ray sensor used
with the CT scanning system of FIG. 1;
FIG. 5 illustrates measurement of an x-ray beam profile with
prior-art detection methods;
FIG. 6 is a flow diagram summarizing methods of the invention in
some embodiments;
FIG. 7 provides an illustration of a typical spectral distribution
of fluence for an x-ray tube; and
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Embodiments of the invention are directed generally to methods and
apparatus for monitoring the operation of diagnostic radiation
systems. While much of the discussion herein focuses on CT imaging
devices, it is to be understood that this is by way of illustration
only. More generally, the principles applied with the invention may
be implemented in a variety of different types of diagnostic
systems that use ionizing sources of radiation.
One example of a CT system 100 adapted in accordance with
embodiments of the invention is illustrated in FIG. 1. In this
drawing, the imaging system is shown generally in the middle of the
drawing and is adapted for irradiation of a patient 104 in a
variety of different modes. Radiation is supplied by a radiation
source 112, which may be an x-ray tube of the type well-known in
the art. Radiation emitted by the source 112 is collimated by a
collimator 116 to direct it towards the patient 104. A filter 120
may optionally be included for spatially varying attenuation of the
generated radiation beam. For example, because the human body is
generally thicker in the middle and narrower around the edges, a
"bowtie" filter may be used to attenuate the radiation beam at its
edges while allowing stronger fluence to propagate near the center
of the beam.
There may be multiple degrees of freedom of motion, both rotational
and translational. Typically, for example the patient 104 is
positioned on a table 108 that may move translationally while the
beam is subject to rotational motion with a gantry 118 to which the
radiation source 112 is coupled. This particular separation of
rotational and translational motion is not a constraint of the
invention, which may be implemented equally well in systems that
may be deployed with other mechanisms for achieved the desired
motion. When the table 108 is moved but the gantry 118 is
stationary, the beam effectively moves translationally through the
patient 104, enabling a series of image slices to be derived. When
the gantry 118 is in motion but the table 108 is stationary, the
beam moves rotationally, enabling multiple orientation images of
structures to be derived to produce an effective three-dimensional
image. These can be combined when both the table 108 and gantry 118
are in motion, producing an effective helical beam used in imaging
the patient. Generally, both types of motion are at constant rates,
although the invention is not limited to such uses and may be
adapted to specialized applications as might be developed for
varying rates of translational and/or rotational motion.
The various components of the structure are controlled with modules
that include a voltage generator 124, a gantry driver 128, a table
driver 132, and an image generator 140 that is interfaced with a
data collection unit 136. The voltage generator 124 provides tube
voltage and current to the radiation source 112 according to
instructions received from a host system 144 described in greater
detail below. The tube current and voltage are provided in
accordance with a mode of operation of the CT system and may vary
for different applications. Specific values of the tube current and
voltage define the fluence intensity emitted by the radiation
source 112. Typical values are 50-150 kV and 100-500 mA, but
embodiments of the invention may also use values outside of these
ranges.
The gantry driver 128 effects rotational motional of the gantry 118
and may be configured to implement a number of different
modalities. For example, the gantry driver 128 may be configured to
rotate the gantry a defined forwards or backwards angle so that
images may be derived with the radiation source 112 in a specific
position relative to the patient 104. Alternatively, the gantry
driver 128 may be configured to rotate the gantry 118 continuously
for a period of time at a predetermined rate. Typical rates may be
around 0.1-2.0 seconds/rotation, but embodiments of the invention
may also use values outside of this range.
The table driver 132 similarly effects translational motion of the
table 108. The principal translational motions effected by the
table driver 132 are in a longitudinal direction, i.e. orthogonal
to the page in the drawing, and may provide both discrete motions
and continuous motions. Specifically, discrete motions may be used
so that the patient 104 is positioned relative to the radiation
source 112 for imaging of a defined portion of the body. Continuous
motions may be used for imaging of a greater portion of the body by
taking slice images as noted above. In addition, it is possible for
the table driver 132 to be configured to effect other translational
motions of the table 108. For instance, the table driver 132 may be
configured to raise or lower the table 108, enabling the patient to
be positioned at a desired distance from the radiation source 112.
This may be particularly useful in accommodating patients of
different sizes so that preferred imaging geometries may be
achieved. In addition, the table driver 132 might also be
configured for transfer motion of the table 108 to further refine
the desired imaging geometry.
The data collection unit 136 may take different positions in
different embodiments, depending particularly on acceptable
scattering angles for the detected radiation being used for image
generation. One position for the data collection unit 136 is
beneath the table 108. The data collection unit 136 may take a
variety of forms, one example of which comprises an array of
radiation-detector elements matched to the spread of a beam
irradiated from the radiation source 112.
The image generator 140 is provided in communication with the data
collection unit 136 to apply processing methodologies to the
collected data in generating an image. Such methodologies may
include such known techniques as volume rendering, multiplanar
reconstruction, minimum-intensity projection, computed-volume
radiography, and the like. For three-dimensional images generated
by the image generator 140, relevant supplementary information is
generally associated. This may include, for example, information
identifying the patient 104. It may also include information
defining a visual point of a three-dimensional image obtained from
the relevant data and a line of sight determined from the visual
point, as well as information of an image-taking direction
corresponding to the line of sight, etc.
These various modules are provided in communication with a control
system, shown in the drawing as comprising a host system 144, an
input device 148, and a display control 152. The host system 144
has access to a storage device 164, which may form part of the
control system or which may be separately accessible by the host
system 144. One function of the host system 144 is to control the
various modules used in defining the imaging geometry, i.e. the
gantry driver 128 and the table driver 132, the voltage generator
124 to define the operational characteristics of the imaging
procedure, and the image generator 140 itself in defining the type
and quality of images to be generated from the procedure.
The host system 144 effects such control by running software that
may additionally obtain input parameters from an operator in
accordance with the type of imaging to be performed so that the
generated images are diagnostically relevant. Such parameters may
be provided through the input device 148, which may take a number
of different forms in different embodiments. For example, the input
device 148 may comprise a touch panel that displays input content
with figures or characters selected by the operator, or might
comprise a keyboard or other type of interface that allows the
receipt of setting values, instructions, and the like from the
operator. The display control 152 interacts with the image
generator 140 to cause a display of the images produced by the
image generator 140 to be shown on a display 156.
The information stored on the data store 164 may vary among
different embodiments. In some instances, the data store 164 is
used exclusively for the storage of information related to
configuring the CT system for an imaging procedure, including
software that is run by the host system 144 and a record of
parameters used to define certain imaging procedures. Such
information includes voltage and current specifications for the
radiation source 112, geometry specifications that include whether
there is to be relative motion between the radiation source 112 and
the patient 104, the type of image to be generated and the
like.
In addition to the various components described above, embodiments
of the invention additionally include one or more sensors
identified generally on the left of the drawing. Such sensors
enable an independent determination parameters relevant to
determining the radiation dose administered to the patient 104
during an imaging procedure. While there may be instances in which
such parameters can be obtained from the control system directly,
the deployment of additional sensors as described here enables such
parameters to be determined without being supplied by the control
system.
A radiation sensor 168 is provided at the output of the collimator
116 and is configured to measure the fluence of the generated
radiation beam. In some instances, the fluence may be measured in a
single dimension, particularly along the longitudinal direction in
which the patient may be moved by the table driver 132.
Alternatively, the fluence may be measured in multiple dimensions,
particularly along the longitudinal direction but also along the
transverse direction, i.e. orthogonal to the longitudinal direction
and parallel to the plane of the table 108. Fluence measurements
are generally taken concurrently with operation of the system,
thereby providing a real-time measurement result of the radiation
intensity exiting the collimator 116. If a bowtie or other type of
filter is incorporated as discussed above, the radiation sensor 168
may be provided at the output of such a filter.
This information may be combined with information derived from
other sensors, which are included with some but not all embodiments
of the invention. For instance, a geometry sensor 172 may be used
to measure the physical separation of different components of the
system, particularly in relation to a position of the patient 104.
A patient-size sensor 176 may similarly be deployed to determine
physical measurements of the patient 104 and a motion sensor 180
may be used to determine rates of rotational or translational
motion of the different components of the system. A
rotational-velocity sensor 182 may determine rates of rotational
motion of the gantry 118. Each of these additional sensors may thus
provide further information relevant in determining the actual
radiation dose administered to the patient when combined with
information from the radiation sensor regarding the fluence of the
radiation beam.
Operation of the various sensors 166, 172, 176, 180, and 182 may be
coordinated with a monitoring system 184. The dashed line in the
drawing indicates that in some embodiments the monitoring system
may be provided in communication with the host system 144, using a
wired or wireless connection. When such communication is provided,
the monitoring system 184 may exchange information with the control
system, such as by using the database 164 coupled with the host
system to store relevant information and/or by obtaining
information about the parameter settings for an imaging procedure.
In cases where such information is available, the monitoring system
184 may use information derived from the sensors as a form of
verification and calibration of dose relationships. As will be
apparent from the discussion below, the sensor information is
capable of providing more accurate dose determinations than the
parameter information used by the host system 144 in configuring
the CT system.
The monitoring system 184 may be one of a plurality of monitoring
systems that are used to monitor different CT systems. This is
illustrated in FIG. 2, which shows a plurality of monitoring
systems 184 in communication with a central system 204 through a
network 200. The network 200 may comprise a public network such as
the Internet in some embodiments, or may comprise a private
network. Because some of the information may be sensitive,
particularly when patient information is included, it is preferable
to use an encryption or other type of security system for
communications between the monitoring systems 184 and the central
system 204 at least when the network 200 comprises a public
network.
With the networked arrangement illustrated in FIG. 2, a database
208 coupled with the central system 204 may be used to integrate
information obtained from different monitoring systems 184. Such
integration may be particularly useful when monitoring systems 184
are being used to collect information from CT systems produced by
the same manufacturer, enabling statistical methods to be applied
to the collected data in improving dose, lifetime, and other
determinations as described below. In addition, when dose
information is associated with particular patient information, the
centralized nature of the database 208 permits lifetime patient
information to be monitored, even when the patient may have imaging
procedures performed at different locations or facilities. Such a
capability allows more accurate information to be provided to
patients and physicians about lifetime exposure to medical-imaging
radiation that may accordingly be a factor in evaluating the risks
of future procedures.
A structure that may be used for each of the monitoring systems 184
is shown schematically in FIG. 3. This drawing broadly illustrates
how individual system elements may be implemented in a separated or
more integrated manner. The monitoring system 184 is shown
comprised of hardware elements that are electrically coupled via
bus 326. The hardware elements include a processor 302, an input
device 304, an output device 306, a storage device 308, a
computer-readable storage media reader 310a, a communications
system 314, and a processing acceleration unit 316 such as a
digital-signal processor or special-purpose processor. The
computer-readable storage media reader 310a is further connected to
a computer-readable storage medium 310b, the combination
comprehensively representing remote, local, fixed, and/or removable
storage devices plus storage media for temporarily and/or more
permanently containing computer-readable information. The
communications system 314 may comprise a wired, wireless, modem,
and/or other type of interfacing connection and permits data to be
exchanged with external devices.
The monitoring system 184 also comprises software elements, shown
as being currently located within working memory 320, including an
operating system 324 and other code 322 that may be loaded into
working memory on bootup or loaded separately. Such other code may
comprise computer programs designed to implement methods of the
invention. It will be apparent to those skilled in the art that
substantial variations may be used in accordance with specific
requirements. For example, customized hardware might also be used
and/or particular elements might be implemented in hardware,
software (including portable software, such as applets), or both.
Further, connection to other computing devices such as network
input/output devices may be employed.
A structure that may be used for the radiation sensor 168 is
illustrated in FIG. 4. This structure comprises a plurality of
scintillating fibers 404 coupled at each end with a photosensor
408. Each scintillating fiber comprises a tube that includes a core
of scintillating material, possibly including additional dopants to
promote scintillation. The scintillating fiber may be made of
plastic, and can be homogeneous or made from a plurality of
different plastics by having an inner core and a cladding sheath.
Scintillating material responds to absorption of radiation by
emitting radiation, usually less energetic than what is absorbed.
This emitted radiation is detected by the photosensors 408 at the
ends of the scintillating fibers, enabling detection of the
incident fluence from the radiation source 112. The light intensity
detected by the photosensors 408 is a function of the energy and
number of photons absorbed, with the number of absorbed photons
itself being proportional to the incident fluence and the length of
the fiber 404 exposed to the radiation. The light thus generated is
converted into an electrical signal for further processing by the
photosensors 408. The electrical signal may be amplified with an
amplifier 412 and digitized with a digitizer 416 for use by the
monitoring system 184.
The use of scintillating fibers advantageously provides a radiation
sensor 168 that can be placed directly in the beam path at the
collimator output, between the radiation source 112 and the patient
104, because it has very low and relatively uniform x-ray
attenuation. This contrasts with conventional detectors that use
electronic components, circuit boards, and the like. Such
structures are made with copper and other heavy metals that
significantly attenuate x rays. By using a
scintillating-fiber-based radiation sensor 168, such materials may
be disposed elsewhere--outside the x-ray beam. Keeping the
electronics out of the x-ray beam also improves the long-term
reliability of the radiation sensor 168 because continuous or
frequent exposure to high-energy photons can damage and degrade
electronic components.
In the illustration, a plurality of fibers 404 are included to
provide a measure of the spatial variation of the fluence. By
monitoring the electrical signals from all of the fibers
concurrently or sequentially, a spatial distribution of the
incident radiation beam in the direction orthogonal to the assembly
is obtained. In an alternative embodiment, a smaller number of
fibers 404 is used and translated across the radiation beam. It is
possible to use only a single fiber 404 when such translation is
used. A two-dimensional beam distribution may be obtained by using
a plurality of the assemblies shown in FIG. 4 oriented at an angle
relative to each other. In a particular such embodiment, two
assemblies are disposed at approximately 90 degrees relative to
each other, enabling the two-dimensional distribution of the
fluence from the radiation source to be determined.
By enabling the detection of spatial information about the beam
without significant attenuation, the structure of the radiation
sensor 168 using scintillating fibers solves an important practical
problem. Conventional alternatives of using an ionization chamber,
for example, suffer from a lack of providing spatial details.
Alternatives of using image-type detectors that provide spatial
information have the disadvantage of greatly attenuating the
primary beam.
FIG. 5 illustrates the raw beam profile generated by the radiation
source 112 in the longitudinal direction. Its length in this
direction depends on the opening size of the collimator 116, but a
prior-art imaging detector is typically narrower than the beam, as
illustrated by the shaded portion of the drawing. Such prior-art
detectors are thus generally incapable of directly measuring the
beam size. The radiation sensor 168 used in embodiments of the
invention can be used for this purpose during calibration for
measuring beam size for smaller collimator openings than maximum.
Even when a patient is being scanned and there can be a large
degree of scatter outside the primary beam, the radiation sensor
168 of the invention enables determining that the collimator 116 is
correctly positioned.
The fiber structure of the radiation sensor 168 is sufficient to
make relative measurements of the beam profile, but it is generally
desirable also to be able to determine the photon-energy value to
enable a calculation of patient dose and air kerma. This may be
achieved with a secondary sensor having a gamma-ray response that
is different from that of the scintillating fibers that make up the
fiber ribbon. If the secondary sensor is disposed within the
primary beam, its attenuation of the beam is preferably low enough
not to compromise the ability of the system software to correct for
that attenuation.
The geometry sensor 172 may take a variety of different forms in
different embodiments, as may the patient-size sensor 176. Each of
these sensors may use any form of technology that allows for
distance or size measurements. Examples include ultrasound
technologies in which acoustic transducers reflect acoustic waves
from structures comprised by the system or from different points on
the body of the patient and use the echo time to determine the
system geometry or the patient size. Other examples include laser
micrometers or visual cameras, among a variety of other distance
and size technologies known to those of skill in the art.
Similarly, there are a variety of known technologies that may be
used to implement motion detection. These include a variety of
mechanical, electromagnetic, and acoustic technologies that may be
used to provide the motion sensor 180. In one embodiment,
accelerometers are used for motion detection.
Methods of the invention are summarized with the flow diagram of
FIG. 6. While the diagram sets forth a number of functions that may
be performed in a particular order, this is not intended to be
limiting. In alternative embodiments of the invention, some
additional functions not specifically identified in the drawing may
also be performed, some of the functions specifically called out
may be omitted, and/or some of the functions may be performed in an
order different from what is set forth. Part of the method includes
determination of a radiation dose administered to a patient as part
of an imaging procedure and may use the structure described above
in connection with FIGS. 1-4.
At block 604, a patient is positioned on the table 108. The patient
104 may take a supine or prone position, or may be placed on her
side, depending on the type of imaging to be performed, i.e.
whether the data are to be collected to generate a single
two-dimensional image, to generate a series of two-dimensional
slice images, or to generate a three-dimensional image. As
previously noted, these different types of images may be generated
using different dynamic configurations of the system. Also relevant
in the positioning of the patient 104 is which tissues or
structures are to be imaged.
The system geometry is measured with the geometry sensor 172 at
block 608 and the patient size is measured at block 612 with the
patient-size sensor 176. After the imaging procedure is begun at
block 616, any motion of the table 108 and/or gantry 118 may also
be measured at block 618, providing a full specification of the
dynamical aspects of the procedure performed on the patient. The
fluence is measured at block 620 with the radiation sensor 168.
An initial check may be performed on the fluence at block 624 to
ensure that the fluence is within normal parameters. The input
arrow to this block identifies that information defining standard
parameter values may be obtained and used in the evaluation. A
deviation from such normal values may prompt the issuance of an
alert at block 628 and potential aborting of the procedure at block
632. Such an alert may take the form of an audible and/or visual
alert so that a technician overseeing the procedure is notified,
and the aborting of the procedure at block 632 may occur
automatically or may result from intervention by such a technician.
The ability to check the fluence at an exit of the radiation source
or collimator permits early intervention, particularly if the
fluence is significantly stronger than an acceptable upper limit.
This allows accidents that might otherwise result from excessive
radiation of a patient to be avoided.
At block 636, a comparison may be made of the measured fluence for
the particular procedure with previous measurements. Such
comparisons are useful in identifying whether there is a systemic
decrease in fluence strength such as may result as the radiation
source ages. Such reduction in tube strength is a known consequence
of tube aging, requiring the use of higher voltage or current to
obtain the desired radiation strength to perform the imaging. If
the fluence shows a pattern of decreasing as checked at block 640,
it is possible to calculate an estimated time to tube failure at
block 644. Such calculations may be performed with a variety of
different models of tube behavior that use any number of
parameters, including the current and voltage applied to the
radiation source 112. Such parameters may also include an
identification of the manufacturer of the radiation source 112
since the performance-decay of tubes may differ in a predictable
way for tubes provided by different manufactures. The models used
in performing such estimates may also make use of past comparisons
of fluence levels, which may be collected for multiple systems and
recorded by the central system 204 for developing such models.
In addition to performing such comparisons during imaging
procedures, the presence of the radiation sensor 168 enables
measurements also to be made during calibration procedures. Such
calibration procedures are typically performed at regular intervals
for each machine, such as by performing a daily calibration. It is
noted that this determination of an estimated time to tube failure
may be performed without direct information being supplied by the
tube manufacturer, allowing an independent check on recommendations
for tube replacement that may be made by manufacturers. At block
648, the estimated time to tube failure is accordingly reported,
allowing the operator of the machine to integrate a plan for
replacement into its normal operating procedures.
At block 652, the patient dose is calculated. The input arrow to
this block identifies that parameters used in determining the
patient dose may be obtained and used in the calculation. Such
calculations may be performed in a number of different ways in
different embodiments. Typically, some kind of modeling technique
is used rather than a direct calculation because of the complexity
of accounting for the different parameters that may impact the
actual dose delivered to a patient. In one embodiment, a Monte
Carlo model is used to calculate the dose from parameters
determined from the measurements collected by the sensors.
Such parameters include the effective voltage kV and the peak
voltage kVp. The peak voltage is the maximum voltage applied across
the x-ray tube, defining the kinetic energy of the electrons
accelerated within the tube and the corresponding peak energy. FIG.
7 provides an illustration of a spectral distribution of a typical
radiation beam that includes a tungsten anode. The distribution has
a characteristic peak at the tungsten k-edge energy E.sub.W and
terminates at a maximum energy E.sub.max, that corresponds to the
peak voltage kVp, but otherwise has a spectral distribution at
different energies. Other types of radiation sources may be used,
such as those that use a molybdenum anode and therefore have
different characteristic peaks. The peak voltage kVp may be
determined by using the secondary sensor having a different
gamma-ray response as described above. For example, FIGS. 8A and 8B
provide illustrations of different responses that two sensors may
have, and the ratio of the responses allows a calculation of the
highest energy photons in the beam, as known to those of skill in
the art.
In addition to kV and kVp, other parameters that may be determined
from sensor measurements and that may accordingly be used in
radiation models to permit calculation of the dose include the
spatial beam intensity profile, the gantry rotation period, and the
patient travel distance, all of which are directly obtained from
the radiation sensor 168 and the motion sensor(s). Parameters such
as the patient-skin--air kerma with or without tube current
modulation may be determined from a combination of patient girth
and imaging geometry as may be obtained from measurements by the
geometry sensor 172 and the patient-size sensor 176. The physical
extent of the dose, i.e. the dose length and the dose volume in
helical scans, may be determined from a combination of geometry
measurements provided by the geometry sensor 172 and table-motion
data as provided by the motion sensor 180.
Models may use these different parameters in combination with a set
of tissue absorption characteristics so that the probability of
absorbing a photon from the beam may be calculated. This
probability is dependent on the photon energy as known from the
energy distribution of the beam, on the spatial distribution of the
beam, on the size of the patient, on the spatial interaction size
between the patient and the beam, and on the patient-skin--air
kerma, each of which is determined as described above. It is noted
that these values may be determined independently from values
calculated by the imaging system itself. Provision of such
independent dose information provides increased safety and enhanced
evidence-based quality assurance information. Additionally,
decoupling the calculation of these safety and performance
parameters from the imaging system itself greatly increases the
probability that system malfunctions, especially those that could
present a patient-safety hazard, are detected.
Returning to FIG. 6, a number of different actions may be taken in
response to calculation of the patient dose. For example, as
indicated at block 656, the patient dose could be output to an
operator of the imaging system as part of providing evaluation
information for the procedure. Alternatively or in addition, the
patient dose may be recorded, as indicated at block 660, in local
and/or central databases, such as central database 208, to provide
a record of cumulative doses that the patient receives. Such
information may aid physicians in evaluating the potential risk of
subsequent imaging procedures to be performed on patients.
Having described several embodiments, it will be recognized by
those of skill in the art that various modifications, alternative
constructions, and equivalents may be used without departing from
the spirit of the invention. Accordingly, the above description
should not be taken as limiting the scope of the invention, which
is defined in the following claims.
* * * * *